Gas chromatographs are used to separate mixtures of gaseous compounds into the individual components and then measure the concentration of each component. The sample to be analyzed is injected into a separation column in a carrier gas that flows through the column. The time needed for a particular chemical component to traverse the column depends on the interactions between the component and the column material. Hence, the components are separated in space as the components move through the column and exit the column at different times. The amount of material leaving the column is measured by some form of detector to provide an analysis of the original sample. The gas then exits the system.
Gas chromatographs often utilize detectors that measure the thermal conductivity of the gas leaving the column. The detectors respond to the changes in thermal conductivity of the gas, and hence, are sensitive to the pressure of the gas at the detector, because thermal conductivity of a gas increases with pressure of the gas. As the sensitivity of the detectors has improved, the sensitivity of the detectors to “noise” resulting from intermittent pressure changes in the room containing the chromatograph has become a problem. For example, if the carrier gas is vented into the room in which the chromatograph is located, pressure fluctuations in the room resulting from doors being opened and closed, or from people moving about the room, are transmitted back to the detector through the gas discharge line. Similarly, if the gas is drawn through the chromatograph and into a disposal cylinder by a vacuum pump, fluctuations in the pump pressure can also be transmitted back to the detector and alter the readings made by the detector.